meninges, ventricles & csf
describe the structure of the meninges
3 layers; dura mater, arachnoid mater & pia mater; meninges of brain and spinal cord are continuous; linked through the foramen magnum; serve a protective function
what is the difference between real and potential space?
A POTENTIAL space is where the layers are normally touching one another. Such a space can be opened if bleeding was to occur. A REAL space is one where there is a GAP between the two layers under normal conditions.
describe arachnoid trabeculae
Arachnoid Trabeculae extend to pia, help to keep brain suspended.
what is cerebrospinal fluid (CSF)?
CSF is made by the choroid plexus. Normally, CSF is a clear, colorless and odourless fluid. The total volume of CSF in an adult is approximately 150mL. CSF has a high turnover, with around 500mL being produced and reabsorbed daily. The function of CSF is to provide mechanical support to the brain, and to protect the brain from changes in pressure. The CSF also controls brain excitability by regulating ionic composition, and removing metabolites. The CSF system has two parts, the elements of which we have already covered. These are known as the internal and external components.
communicating hydrocephalus
For COMMUNICATING hydrocephalus (or non-obstructive hydrocephalus), there is NO OBSTRUCTION of the ventricles. COMUNICATING hydrocephalus is caused by impaired cerebrospinal fluid REABSORBTION. It has been theorized that this is due to functional impairment of the arachnoid granulations. Various neurologic conditions may result in communicating hydrocephalus, including meningitis, subarachnoid or intraventricular hemorrhage.
what are the 4 major subarachnoid cisterns?
Interpeduncular cistern - is situated at the base of the cerebral hemispheres, between the two temporal lobes, and contains the optic chiasma. Pontine cistern - surrounds the anterior aspect of the pons. Quadrigeminal cistern - is posterior to the midbrain. Cerebellomedullary cistern - the largest cistern - lies between the cerebellum and the medulla.
non-communicating hydrocephalus
NON-COMMUNICATING hydrocephalus occurs when CSF outflow is obstructed. NON-COMMUNICATING hydrocephalus may be accompanied by a range of symptoms including downcast eyes, irritability, seizures, drowsiness, and vomiting. If the skull is still pliable, as it is in most children younger than 2 year, the head may enlarge.
subdural space
Subdural space is also a POTENTIAL space (that is, it is not normally present). It may be opened up by blood from a vein that tears as it crosses the arachnoid to enter a dural sinus.
describe the potential need for CSF pathology (HIGH YIELD*****)
Yellow discolouration of CSF indicates pathology, and this can include bacterial meningitis, tuberculous meningitis, or fungal meningitis. Alterations to turbidity and viscosity are also signs of pathology. Increased neutrophil, lymphocyte and proteins, and decreased glucose content are indicators of pathology.
epidural hematoma source of blood
meningeal artery
what is tentorial notch?
opening in tentorium cerebelli that surrounds midbrain
what is falx cerebelli?
separates cerebellum hemispheres
what is the external part of the CSF system?
subarachnoid spaces and cisterns
describe arachnoid mater
thin, delicate, avascular, attached to dura, semitransparent;
describe intraparenchymal hemorrhage
(IPH) is one extension of intercerebral hemorrhage with bleeding within brain parenchyma (meaning the functional areas of the brain). IPH accounts for ~8-13% of all strokes and results from a wide spectrum of disorders. IPH is more likely to result in potentially fatal herniation, death or major disability than subarachnoid hemorrhage, and therefore constitutes an immediate medical emergency.
describe intraventricular hemorrhage
(IVH) is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space. It can result from physical trauma or from hemorrhaging in stroke. IVH occurs in about 35% of moderate to severe traumatic brain injuries and can lead to potentially fatal herniation.
describe subarachnoid space
Subarachnoid space filled with CSF. - Subarachnoid cisterns openings in the subarachnoid space created by separation of arachnoid and pia mater. Filled with CSF.
describe the blood supply of the choroid plexus
The choroid plexus receives its blood supply from the choroidal arteries. Anterior choroidal artery - which (most commonly) originates from the internal carotid artery. Medial posterior choroidal artery. Lateral posterior choroidal artery - usually both arise from the posterior cerebral artery (PCA).
subdural hematoma
When bleeding occurs between the DURA and the ARACHNOID, it is called an subdural hematoma. Subdural hematomas are typically crescent shaped, and expansion follows the curve of the brain and skull. Subdural hematomas do not cross the midline because they cannot get past the falx cerebri. However, they may shift midline structures.
epidural hematoma
When bleeding occurs between the DURA and the SKULL, it is called an epidural hematoma. Epidural hematomas have a convex/lens shape, they may cross the midline, and expansion is inward toward the brain.
describe arachnoid villi
allow passage of CSF from subarachnoid space into dural venous sinus; Large arachnoid villi are called arachnoid granulations.
describe subarachnoid hemorrhage
bleeding into the subarachnoid space and can occur spontaneously (usually from a ruptured cerebral aneurysm) or may result from head injury.
describe the fourth ventricle
cerebellum posteriorly; pons and rostral medulla anteriorly; shaped like a tent with a double peaked roof
subarachnoid, intraparenchymal, and intraventricular hemorrhage source of blood
cerebral artery or vein
cranial meninges
dura: double layered, attached to inner skull surface; epidural space: potential space between dura and skull; arachnoid: attached to inner surface of dura; pia mater: attached to CNS surface;
spinal meninges
dura: single layered, suspended in vertebral canal; epidural space: real space between dura and vertebral periosteum; arachnoid: attached to inner surface of dura; pia mater: attached to CNS surface, expanded as denticulate ligaments
subdural or epidural hematoma source of blood
dural venous sinus
describe the path of the median aperture (foramen of magendie)
from: fourth ventricle; to: cerebellomedullary cistern (cistern magna); From the fourth ventricle, connections are made to the subarachnoid space via the Median aperture (or Foramen of Magendie), which connects to the cerebellomedulary cistern; A block at any of these passages leads to dilation of one or more ventricles, as CSF outflow is obstructed.
describe the path of the inter ventricular foramina (foramen of monro)
from: lateral; to: third ventricle: The left and right interventricular foramina (or Foramen of Monro) connect the lateral ventricles with the third ventricle. A block at any of these passages leads to dilation of one or more ventricles, as CSF outflow is obstructed.
describe uncal herniation
herniation as a result of pressure from an expanding mass in one temporal lobe Part of the medial temporal lobe (called the uncus) can herniate through the tentorial notch and press the midbrain against the free edge of the tentorium. The midbrain contains structures essential for consciousness, and this type of herniation typically produces coma, often followed by death. This is called an uncal herniation.
what is the internal part of the CSF system?
lateral ventricles, inter ventricular foramens, third ventricle, cerebral aqueduct, four ventricle;
subdural hematoma source of blood
vein at attachment to sinus
what are the 4 major dural venous sinuses?
4 major sinuses: superior sagittal sinus - at the top (of course, it is "superior"), between the hemispheres. straight sinus - between the cerebral hemispheres, and sitting above the cerebellum. transverse sinus (left and right) - moving laterally away from the confluence. sigmoid sinus (left and right, S-shaped) - forming an S-shape and draining down into the internal jugular vein. The superior sagittal sinus, straight sinus, and transverse sinus meet in the confluence of the sinuses, and it is the sigmoid sinus that empties into the internal jugular vein.
describe the CSF circulation
CSF is made in the choroid plexus. From here, the CSF enters the ventricles (recall the 4 ventricles). Next the CSF moves into the subarachnoid space. To exit the subarachnoid space, the CSF travels through the arachnoid villi (large villi are known as arachnoid granulations). The arachnoid villi allow the CSF to pass into the sinuses (recall the 4 major sinuses, and four minor sinuses). From the sinuses, the CSF is finally drained into the internal jugular vein.
describe the arachnoid villi as a CSF-blood barrier
In the meninges, the blood vessels of the dura are fenestrated and provide little barrier function. However, the outer cells of the arachnoid membrane have tight junctions and this cell layer forms the physical barrier between the CSF-filled subarachnoid space and overlying structures. The blood vessels between the arachnoid membrane and the pial surface have tight junctions. There is evidence that absorption of CSF by the arachnoid villi occurs by a valve-like process, permitting the one-way flow of CSF from the subarachnoid spaces into the venous sinuses.
what is lumbar puncture?
It is possible to test the composition of the CSF by performing a lumbar puncture. This procedure involves the insertion of a spinal needle into the subarachnoid space surrounding the cauda equina. The lumbar cistern extends from the caudal end of the spinal cord (conus medullaris) to the second sacral vertebra (S2). The subarachnoid space (widest in this region) contains the filum terminale internum (a thin filament). The subarachnoid space in the lumbar cistern also contains the cauda equina (a bundle of nerve roots of all the spinal nerves caudal to the second lumbar vertebra). To compensate for growth, a lumbar puncture is performed at L3/L4 in the adult, and L4/L5 for children. A lumbar puncture can be performed either with the patient sitting with their head and shoulders bent forward, or with the patient lying in a left or right lateral position with their neck bent in full flexion and knees bend in full flexion up to their chest, approximating the fetal position.
what is choroid plexus?
Projections of pia mater into the ventricles of the brain are called choroid plexus. Areas where pia and ependyma are directly applied to each other form part of the choroid plexus. CSF is made by the choroid plexus. The choroid plexus receives its blood supply from the choroidal arteries.
adding dura septa and sinuses...
The SUPERIOR SAGITTAL sinus runs along the superior border of the falx cerebri. The INFERIOR SAGITTAL sinus courses along the inferior border of the falx cerebri, superior to the corpus callosum. The STRAIGHT sinus is situated where the falx cerebri meets the midline of the tentorium cerebelli. The TRANSVERSE sinus sits in the attached margin of the tentorium cerebelli. This is a great diagram to help you conceptualize the relationship between these key elements of the Dura.
what are the distinctive differences between cranial and spinal meninges?
The cranial meninges are continuous with the spinal meninges through the foramen magnum. However, one important distinction between cranial and spinal meninges is that cranial DURA mater consists of TWO layers, and ONLY ONE of these is continuous through the foramen magnum. Cranial dura mater has TWO layers - a superior/periosteal layer, and a deep meningeal layer, which is the "actual" dura mater. Only the meningeal cranial dura mater layer continues through the foramen magnum and forms the spinal dura mater.
what are denticulate ligaments?
The denticulate ligaments extend from the pia mater to attach THROUGH the arachnoid TO the dura mater to anchor the spinal cord to its dural sheath. The denticulate ligaments are in pairs, with one either side of the spinal cord. There are 21 such pairs and these provide support to the spinal cord within the vertebral column.
describe the choroid plexus as a CSF-blood barrier
The endothelial cells of choroid plexus blood vessels are fenestrated and form a non- restrictive barrier between the cerebrospinal fluid (CSF) and blood vessel. The epithelial cells have apical tight junctions that restrict intercellular passage of molecules.
epidural space
The epidural space is a POTENTIAL space (that is, it is not normally present) between the dura and skull It may be opened up by blood from a ruptured meningeal artery or, less commonly, a torn dural venous sinus.
subarachnoid space
The subarachnoid space is an ACTUAL space. It is normally present, and filled with CSF. Bleeding can open up potential meningeal spaces!
what is the CSF-blood barrier?
The two "barriers" in the CSF- blood barrier are at the choroid plexus, and the arachnoid villi. The idea is to protect the brain.
what are dural venous sinuses?
found between layers of dura mater, receive blood from veins of brain, receive cerebrospinal fluid from subarachnoid space, ultimately empty into internal jugular vein; The dural venous sinuses are found between layers of the dura mater and form several vein-like sinuses that carry blood (which has already given its supply of oxygen and nutrients to the brain) back to the heart. In addition to receiving blood from internal and external veins of the brain, these sinuses receive cerebral spinal fluid (CSF) from the subarachnoid space, and ultimately empty into the internal jugular vein.
describe the path of the lateral aperture (left and right; foramen of luschka)
from: fourth ventricle; to: quadrigeminal cistern (superior cistern/cistern of the great cerebral vein); the left and right Lateral aperture (or Foramen of Luschka), which connects to the quadrigeminal cistern. A block at any of these passages leads to dilation of one or more ventricles, as CSF outflow is obstructed.
describe the path of the cerebral aqueduct (aqueduct of sylvius)
from: third ventricle; to: fourth ventricle; The cerebral aqueduct (or Aqueduct of Sylvius) connects the third ventricle with the fourth ventricle. A block at any of these passages leads to dilation of one or more ventricles, as CSF outflow is obstructed.
describe cingulate herniation
herniation as a result of pressure from a hematoma One cingulate gyrus can slip under the falx cerebri and press on the opposite cingulate gyrus; this can happen with no serious neurological consequences. This is called a cingulate herniation (also called an subfalcine herniation).
describe tonsilar herniation
herniation as a result of pressure from an expanding cerebellar mass One tonsil of the cerebellum can herniate through the foramen magnum, compressing the medulla against the margin of the foramen. The medulla contains respiratory and cardiovascular centers, and pressure on it is usually rapidly fatal. This is called a tonsilar herniation.
what are the 4 minor sinuses?
inferior sagittal sinus - is inferior to the superior sagittal sinus (that makes sense!), the INFERIOR sagittal sinus courses along the inferior border of the falx cerebri, superior to the corpus callous. occipital sinus - situated in the attached margin of the falx cerebella. inferior petrosal sinus (left and right) - joins with the sigmoid sinus to form the internal jugular vein, which continues inferiorly to drain blood from the base of the skull. superior petrosal sinus (left and right) - passes backward and laterally to drain into the transverse sinus.
describe the lateral ventricle
left and right; curve through each cerebral hemisphere; 5 parts: anterior horn, body, posterior horn, inferior horn, atrium
describe the third ventricle
midline cavity in the diencephalon; doughnut-like shape; "hole" corresponds to interthalamic adhesion
what is dura septa?
separate cranial cavity compartments; restrict brain from displacement; falx cerebri, falx cerebelli, tentorium cerebelli (tentorial notch); The function of the Dura Septa is to separate the cranial cavity into compartments and protect the brain from displacement. There are three distinct Dura Septa. The FALX CEREBRI separates the hemispheres of the cerebrum. The FALX CEREBELLI separates the hemispheres of the cerebellum. The TENTORIUM CEREBELLI separates the cerebrum from the cerebellum. The TENTORIAL NOTCH is the opening in the tentorium cerebelli which surrounds the midbrain.
what is tentorium cerebelli?
separates cerebrum from the cerebellum
what is falx cerebri?
separates cerebrum hemispheres
describe pia mater
thin and delicate, richly vascularized, closely adheres to all external surfaces of CNS, projections of pia mater into brain ventricles are called choroid plexus.
describe dura mater
tough and inflexible; pain sensitive; has own blood supply; dura septa & dural venous sinuses; Dura mater has two layers: The superficial layer (also called the periosteal layer), which serves as the skull's inner periosteum, called the endocranium. The deep layer is called the meningeal layer; the actual dura mater. The Dura mater is tough and inflexible. Dura means "hard" in latin. Dura mater is pain sensitive, and has it's own blood supply. The two main components of the Dura mater are the Dura Septa, and the Dural Venous Sinuses.